1. Field of the Invention
The present invention relates to a laminated electronic component, and more particularly, to a laminated electronic component which includes an external terminal electrode formed directly by plating so as to be electrically connected to an internal electrode.
2. Description of the Related Art
As shown in FIG. 2, a laminated electronic component 101 as typified by a laminated capacitor includes a laminate 105 including a plurality of stacked insulator layers 102 and a plurality of internal electrodes 103 and 104 formed along the interfaces between the insulator layers 102. The ends of the plurality of internal electrodes 103 and the ends of the plurality of internal electrodes 104 are respectively exposed at the end surfaces 106 and 107 of the laminate 105, and external terminal electrodes 108 and 109 are arranged so that the respective ends of the internal electrodes 103 and the respective ends of the internal electrodes 104 are electrically connected to each other.
For the formation of the external terminal electrodes 108 and 109, typically, a metal paste including a metal constituent and a glass constituent is applied onto the end surfaces 106 and 107 of the laminate 105, and then fired to form paste electrode layers 110. Next, first plating layers 111 including, for example, nickel as their main constituent are formed on the paste electrode layers 110, and second plating layers 112 including, for example, tin or gold as their main constituent are formed on the first plating layers 111. More specifically, each of the external terminal electrodes 108 and 109 is made of a three-layer structure including the paste electrode layer 110, the first plating layer 111, and the second plating layer 112.
The external terminal electrodes 108 and 109 are required to provide favorable solderability when the laminated electronic component 101 is mounted on a substrate using solder. At the same time, the external terminal electrode 108 is required to electrically connect the plurality of internal electrodes 103 to each other, which are electrically insulated from each other, and the external terminal electrode 109 is required to electrically connect the plurality of internal electrodes 104 to each other, which are electrically insulated from each other. The second plating layer 112 described above ensures solderability, and the paste electrode layer 110 electrically connects the internal electrodes 103 and 104 to each other. The first plating layer 111 prevents solder leach at the solder joint.
However, each of the paste electrode layers 110 has an increased thickness of several tens μm to several hundreds of μm. Therefore, in order to achieve the dimensions of the laminated electronic component 101 within certain specifications, there is an undesirable need to reduce the effective volume for providing the capacitance, because there is a need to provide a certain volume of the paste electrode layers 110. On the other hand, each of the plating layers 111 and 112 has a thickness on the order of several μm. Thus, if the external terminal electrodes 108 and 109 can be made of only the first plating layer 111 and the second plating layer 112, the effective volume for providing the capacitance can be significantly increased.
For example, Japanese Patent Application Laid-Open No. 63-169014 discloses a method of forming an external terminal electrode by depositing a conductive metal film via electroless plating onto the entire sidewall surface of a laminate at which internal electrodes are exposed, so as to short-circuit the internal electrodes exposed at the sidewall surface.
However, when a conductive metal film defining an external terminal electrode is formed by electroless plating, the film has small crystal grain sizes of metal grains, and has a surface that is susceptible to oxidation. Therefore, in the case of forming a first plating layer by electroless plating with the use of a metal, for example, including copper as its main constituent, and then forming a second plating layer thereon including nickel as its main constituent, peeling is likely to occur between the first plating layer and the second plating layer. In addition, electroless plating has a relatively low deposition rate, which prevents an increase in productivity.
On the other hand, in order to solve the problems of the electroless plating described above, it is conceivable to apply electrolytic plating, although not described in Japanese Patent Application Laid-Open No. 63-169014. However, with electrolytic plating, the degree of plating growth (the throwing power of the plated deposition) is inferior as compared to electroless plating. Thus, there is a possibility that the increased distance between adjacent exposed ends of the internal electrodes may produce insufficient plating growth, and thus produce a portion which is not plated.